1、Designation: C1812 15Standard Practice forDesign of Journal Bearing Supports to be Used in FiberReinforced Concrete Beam Tests1This standard is issued under the fixed designation C1812; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice prescribes the design of journal-bearingtype rollers to support each end of fiber-reinfor
3、ced concretebeams tested using Test Method C1399/C1399M or TestMethod C1609/C1609M. The roller design is intended toprovide a consistent and relatively low value of effectivecoefficient of friction at the beam supports. The bearing designincorporates metal-on-metal sliding surfaces lubricated withgr
4、ease.NOTE 1During the progress of a test, a crack or cracks open on theunderside of the beam between the loaded third points causing theunderside of each portion of the beam to move away from the center. Thedesign is intended to provide for unlimited rotation of the roller at thepoint of contact wit
5、h the test beam in response to this motion.NOTE 2The design of the supporting rollers is a significant factor indetermining the magnitude of the arching forces that cause error inflexural test results.2Improperly designed supporting rollers can influencethe apparent flexural behavior of fiber-reinfo
6、rced concrete beams.3Theeffective coefficient of friction can be determined using a method similarto that described by Bernard.41.2 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. Thevalues stated in each system may not be exact equivalents;th
7、erefore, each system shall be used independently of the other.Combining values from the two systems may result in non-conformance with the standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this st
8、andard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:5C125 Terminology Relating to Concrete and Concrete Ag-gregatesC1399/C1399M Test Method for Obtaining AverageResidual-Strengt
9、h of Fiber-Reinforced ConcreteC1609/C1609M Test Method for Flexural Performance ofFiber-Reinforced Concrete (Using Beam With Third-PointLoading)D4950 Classification and Specification for Automotive Ser-vice Greases2.2 SAE International Standard:6J 404 Chemical Composition of SAE Alloy Steels3. Termi
10、nology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 effective coeffcient of friction, na dimensionlessratio of the horizontal force required to initiate rotation of theroller support applied at
11、the contact point between the rollerand test beam divided by the normal force applied at the samepoint (see Fig. 1).3.2.2 roller, na journal bearing capable of continuousrotation without exhibiting a significant variation in resistanceto rotation.4. Significance and Use4.1 The presence of friction i
12、n the supporting rollers usedwhen testing a fiber-reinforced concrete beam will increase theapparent load resistance of the beam. Roller supports designed1This practice is under the jurisdiction of ASTM Committee C09 on Concreteand ConcreteAggregates and is the direct responsibility of Subcommittee
13、C09.42 onFiber-Reinforced Concrete.Current edition approved July 1, 2015. Published September 2015. DOI:10.1520/C1812-15.2Zollo, R. F., 2013. “Analysis of SupportApparatus for Flexural Load-deflectionTesting: Minimizing Bias,” Journal of Testing and Evaluation, ASTM International,Vol. 41, No. 1, pp.
14、 1-6.3Wille, K. and Parra-Montesinos, G.J., 2012. “Effect of Beam Size, CastingMethod, and Support Conditions on Flexural Behavior of Ultra-High-PerformanceFiber-Reinforced Concrete,” ACI Journal of Materials, Vol. 109, No. 3, pp.379-388.4Bernard, E.S., 2014. “Influence of friction in supporting rol
15、lers on the apparentflexural performance of third-point loaded fibre reinforced concrete beams,”Advanced Civil Engineering Materials, ASTM International Vol. 2, No. 1, pp.158-176.5For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
16、 For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.6Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,PA 15096, http:/aerospace.sae.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
17、shohocken, PA 19428-2959. United States1in accordance with this practice will provide a relatively lowand consistent value of friction at the supports.4.2 Two types of rollers are used to support a beam. Oneincludes a cylindrical bearing that allows the roller assembly torotate along an axis paralle
18、l to the longitudinal axis of the beamand thereby accommodate any warping introduced duringspecimen fabrication. The other roller does not include thecylindrical bearing.4.3 The rollers are designed for use with 150 mm 6 in. or100 mm 4 in. deep beams of square cross-section.4.4 A method is provided
19、for correcting the apparent loadresistance measured using the roller with a known value of theeffective coefficient of friction of the roller supports to obtainan estimate of the load resistance in the absence of friction.5. Apparatus5.1 GeometryA pair of rollers is required to support abeam during
20、a test. The barrel of each roller, which is thatportion of the roller in contact with the beam, shall be free torotate about an axis perpendicular to the longitudinal axis ofthe beam to accommodate movement of the initial supportpoint on the beam away from the center during a test. Frictionbetween s
21、liding surfaces within each roller will generate asmall resistance to rotation of the barrel relative to themounting (see Fig. 1). A roller fabricated in accordance withthis practice will exhibit an effective coefficient of friction ofabout 0.10.4Journal bearing supports manufactured in confor-mance
22、 with this practice do not need to be tested to confirmthat the effective coefficient of friction meets requirements.5.1.1 One of the two rollers supporting the underside of thebeam shall be able to rotate about an axis parallel to thelongitudinal axis of the beam to accommodate a warped testbeam su
23、rface that could induce torsion in the beam duringtesting (see Note 3 and Fig. 2). The other roller shall be fixedagainst rotation about a longitudinal axis to prevent the beamfrom overturning during installation and testing (see Fig. 3).Rotation about a longitudinal axis shall be accommodated byinc
24、lusion of a cylindrical bearing surface under the rollermount with a center of rotation that coincides with the plane ofthe contacting surface between roller and bottom of the beam.The base of the cylindrical bearing surface shall include boltPL= frictional force applied to the roller by the beam.PV
25、= vertical force applied to the roller by the beam.FIG. 1 Forces Acting on a Supporting Roller During a TestFIG. 2 General Arrangement Drawing of Supporting Roller with a Cylindrical Bearing BaseC1812 152holes to facilitate fixing the roller to the testing machine. Theroller that is fixed against ro
26、tation about a longitudinal axis(Fig. 3 and Fig. 6) shall incorporate a similar mounting so thatthe total height is the same as the roller assembly shown in Fig.2 and Fig. 5 and the beam is maintained level during a test. Thebarrel of each roller is fabricated from one piece of steel. Capssecure the
27、 roller barrel in place so that it may rotate but notdisplace during a test. The cylindrical seat of the roller that isfree to rotate about a longitudinal axis shall include a flangeand a recess as shown in Fig. 4 to prevent longitudinaltranslation during testing.NOTE 3The upper half of the cylindri
28、cal bearing surface is not fixedto the lower half, but is restrained by guides intended to prevent the upperpart of the bearing from sliding in the longitudinal direction in response tothe forces imposed by the beam as it deflects at the bottom surface andeach half of the beam moves away from the ce
29、nter as the crack(s) widen.NOTE 4To check that a properly manufactured and lubricated journalbearing assembly is functional, the rotating roller within the assemblymust turn at least 360 without undue resistance when turned by hand.Such a check should be performed before each test is undertaken.5.2
30、Steel GradeThe rollers and their correspondingmountings shall be fabricated using SAE 4140 alloy steel orequivalent.5.3 Surface TreatmentThe sliding and rotating surfaces ofthe roller, bushings, and cylindrical bearing within the supportmounting shall be machined to a high-grade machine finishwith a
31、 roughness average of 0.8 m 32 in. or better. Thedifference in radius between the contacting surface of the rollerbarrel and the corresponding contacting surface of the bushingis limited to 0.10 mm 0.004 in.5.4 LubricationThe design includes grease ports for lu-bricating the sliding surfaces. Grease
32、 shall be applied to thesurfaces via the grease ports to limit friction and expel debristhat may collect at the junctions between the shaft of the rollerand the bushing caps. The user shall establish a schedule forgrease application to ensure proper operation of the rollerassemblies. The grease shal
33、l be National Lubricating GreaseInstitute (NLGI) Grade 2 lithium complex molybdenum disul-phide high-pressure grease as described in Specification D4950or equivalent.5.5 Mounting of Rollers within Testing MachineThemounting shall include a 25 mm 1 in. thick steel plate withbolts located so as to sec
34、ure the roller supports to the testmachine during testing. The designs shown in Figs. 2-6incorporate four bolt holes in the base of the bearing mountwith an overall height of roller and mount equal to 100 mm4.0 in. These dimensions have been found to performsatisfactorily in service, but the exact d
35、imensions of the basesare permitted to be altered to suit the dimensions of the testmachine to which they are fixed.5.6 DimensionsThe dimensions of the rollers shown inFigs. 5 and 6 are based on SI units. Equivalent dimensions ininches are listed in Table 1. Tolerances on dimensions are 60.1 mm 0.00
36、4 inches.6. Keywords6.1 fiber-reinforced concrete; flexural performance; friction;post-crack; residual strength; roller supportsFIG. 3 General Arrangement Drawing of Supporting Roller with a Fixed Bearing BaseC1812 153FIG. 4 Exploded View of Roller Assembly Showing Bushing Caps to Secure Roller Barr
37、el and Flanges to Prevent Sliding in the Longitu-dinal DirectionC1812 154FIG. 5 Sectional View of Roller on Cylindrical Bearing Base with Dimensions in mmFIG. 6 Sectional View of Roller on Fixed Bearing Base with Dimensions in mmC1812 155APPENDIX(Nonmandatory Information)X1. CORRECTION OF TEST RESUL
38、TS FOR FRICTION IN SUPPORTSX1.1 ScopeX1.1.1 This appendix provides recommendations for cor-rection of flexural strength results obtained in beam tests whenan effective coefficient of friction of known magnitude ispresent in the supporting rollers under a beam subject tothird-point loading.X1.1.2 The
39、 correction method may be applied to all valuesof load resistance obtained prior to and after cracking of theconcrete matrix in the beam test.X1.2 CalculationX1.2.1 Apparent Load Resistance of BeamFig. X1.1 is aTABLE 1 List of Dimensions in SI Units and Equivalents inInchesDimension in millimetres D
40、imension in inches1 0.047 0.288 0.3212 0.5015 0.5918 0.7120 0.7921 0.8325 1.0034 1.3438 1.5040 1.5850 2.0065 2.5670 2.7675 3.0090 3.50120 4.72150 6.00FIG. X1.1 Free-Body Diagram for a Third-Point Loaded Beam with Off-Center Crack and an Effective Coefficient of Friction Equal to atEach Supporting Ro
41、llerC1812 156free-body diagram of the cracked portion of a beam for whichthe effect of friction on the apparent load resistance can beevaluated. The ratio, , of the apparent load resistance, PF,ofa third-point loaded beam in the presence of friction within thesupporting rollers to the load resistanc
42、e of the same beam in theabsence of friction, P0, is found as: 5PFP05LL 2 3 d!(X1.1)where:L = beam span, mm in., = effective coefficient of friction of the roller support,dimensionless, andd = beam depth, mm in.For Test Methods C1399/C1399M and C1609/C1609M, d =L/3, thus the ratio for a third-point
43、loaded beam is expressedas: 511 2 !(X1.2)X1.2.2 Correction of Apparent Load ResistanceThe valueof is equal to 1.11 for an effective coefficient of friction, , ina roller support under a third-point loaded beam equal to 0.10.To remove the error introduced by the presence of friction inthe rollers, th
44、e corrected load resistance of the beam is foundas:P05 PF (X1.3)X1.2.3 Application of Correction FactorIf a roller con-forming to the design prescribed in this practice is used tosupport each end of a third-point loaded beam, the effectivecoefficient of friction can be taken to equal 0.10 assuming t
45、herollers are regularly cleaned and maintained. The correction tothe load resistance of the beam indicated by Eq X1.3 is thenapplied to all points of the recorded load-deflection record.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any
46、item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical c
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